The challenge, if successful, could greatly shake up the next round of Senate elections in 2014.

Lawmakers tried to thwart the challenge from the League of Women voters and other groups, who say Senate Republicans redrew districts for partisan advantage in violation of voter-approved "fair districts" amendments to the Constitution.

Lawmakers argued that only the Supreme Court had the power to review legislative redistricting maps, in a narrow 30-day window last year.

But in a 5-2 ruling, the court said that state law and its own precedents mean the case must proceed in a circuit court in Tallahassee.

Writing for the majority, Justice Barbara Pariente said last year's brief and compressed "facial" review of maps was not intended to be the last word on the issue as it held in previous redistricting challenges in 1972, 1982 and 1992.

"Our precedent remains clear that subsequent challenges based on factual evidence not considered or available in this court's initial 30-day review may be brought and argued in a court of competent jurisdiction," Pariente wrote. "These are the exact types of claims that must be subject to a fact-finder's scrutiny."

Chief Justice Ricky Polston and Justice Charles Canady dissented.

Senate President Don Gaetz, R-Niceville, who chaired the Senate Reapportionment Committee that drew the maps, said he was disappointed in the ruling and stands by the maps, which he said are "compliant with Florida's Constitution (and) will ultimately be affirmed."

Praising the ruling, the League of Women Voters said: "When districts are manipulated, voters are disenfranchised."

The ruling ensures that the costs to taxpayers to defend the 2012 redistricting maps will mount, as noted by Senate lawyer Raoul Cantero, a former Supreme Court justice, who predicted "perhaps endless rounds of litigation."

The Supreme Court last year approved the redrawing of all 120 House districts, but found the new Senate map was "rife with indicators of improper intent" and violated standards that bar favoritism toward incumbents or parties, even in the way district numbers were assigned.

A redrawn Senate map won court approval, and senators were assigned district numbers in a random lottery-style drawing.

Democrats picked up two Senate seats in the 2012 elections and Republicans now hold 26 of 40 seats. But of 20 Senate seats up for grabs next year, 16 are held by Republicans and four by Democrats.